1. Field of the Invention
The present invention relates to an orbital machining apparatus for producing a hole in a workpiece by way of a cutting tool rotating about its own tool axis as well as eccentrically (orbiting) about a principal axis corresponding to the longitudinal center axis of the hole to be machined. More particularly, the present invention relates to an improved mechanism of an apparatus for transferring a rotational movement to an inner eccentric cylindrical body of a mechanism for adjusting the radial offset (orbit radius) of the cutting tool axis relative to the principal axis.
2. Description of the Related Art
WO 03/008136 A1 discloses an orbital machining apparatus for producing a hole in a workpiece by way of a cutting tool. The apparatus includes a first actuator configured for rotating the cutting tool about its longitudinal center axis during the machining of the hole. A second actuator is configured for moving the cutting tool in an axial feed direction substantially parallel to the tool axis, the second actuator being simultaneously operable with the first actuator. A third actuator is configured for rotating the cutting tool about a principal axis, the principal axis is substantially parallel to the center axis of the tool and coaxial with a longitudinal center axis of the hole to be machined. The third actuator is simultaneously operable with the first and second actuators. A radial offset mechanism is configured for controlling the radial distance of the center axis of the cutting tool from the principal axis, the radial offset mechanism includes an inner cylindrical body having an eccentric cylindrical hole. The eccentric hole has a longitudinal center axis that is parallel to and radially offset from a longitudinal center axis of the inner body. The eccentric hole is configured to radially and rotatably support a spindle unit for operating the cutting tool. An outer cylindrical body has an eccentric cylindrical hole. The eccentric hole of the outer body has a longitudinal center axis that is parallel to and radially offset from a longitudinal center axis of the outer body. The inner cylindrical body is radially supported in the eccentric hole of the outer cylindrical body and rotatable therein so as to allow for adjustment of the radial distance of the center axis of the cutting tool from the principal axis. The third actuator includes a first motor drivingly connected to the outer cylindrical body for individually rotating the latter about the longitudinal center axis thereof, and a second motor drivingly connected to the inner cylindrical body for individually rotating the latter about the longitudinal center axis thereof. The first and second motors are configured to rotate the outer and inner cylindrical bodies in synchronism to maintain a mutual rotary position thereof so as to keep the radial offset position of the cutting tool unchanged during a working operation.
The first and second motors are also configured to rotate the outer and inner cylindrical bodies in different angular speeds so as to vary the radial offset position of the cutting tool. Thus, two separate motors and the transmissions are configured for rotating the outer and inner cylindrical bodies either in synchronism (=no mutual rotation) during a working operation to maintain a predetermined mutual rotary position of the cylindrical bodies and thereby a predetermined radial offset (for making a cylindrical hole or recess in a workpiece), or in different angular speeds (mutual rotation) to vary the radial offset either during a working operation (e.g. for making a conical hole or recess) or during a non-working phase to adjust the radial offset to another desired radial offset value.
The transmission or mechanism for transferring a rotational movement from the second motor to the inner cylindrical body includes a coupling, which is configured for allowing the inner cylindrical body to perform an orbital movement about the principal axis while not rotating about its own center axis relative to the outer cylindrical body. The coupling also permits the inner cylindrical body to be rotated about its center axis relative to the outer cylindrical body by the second motor so as to vary the radial offset either during a working operation or during a non-working phase to adjust the radial offset to another desired radial offset value. This coupling comprises a fork-and-cam roller mechanism.
A problem related to the fork-and-cam roller mechanism is that the contact surface of the cam roller wears with time and creates a play, which affects the degree of precision of the coupling mechanism and thus of the working process of the orbital machining apparatus.